Laravel 5.1 - Store Data in Eloquent: Relationships - laravel

Question

I folowing Official Laravel 5.1 User Authentication to create User Login and User Register and it is run well.
But now, I add another table, user_detail table, which contain another data of user like first/last name, gender, etc. This table has one to one relationship with user table. And I already defining relationships like hasOne and belongsTo.
I want to ask, how when I registered a new user, the both user and user_detail table is filled? Although the user_detail tables just filled in the 'id' only, because the user table and user_detail table have same id for primarykey and foreignkey.
For reference here my routes:
...
// Registration routes...
Route::get('auth/register', 'Auth\AuthController#getRegister');
Route::post('auth/register', 'Auth\AuthController#postRegister');
...
AuthController:
<?php
namespace App\Http\Controllers\Auth;
use App\User;
use App\UsersDetail;
use Validator;
use App\Http\Controllers\Controller;
use Illuminate\Foundation\Auth\ThrottlesLogins;
use Illuminate\Foundation\Auth\AuthenticatesAndRegistersUsers;
class AuthController extends Controller {
/*
|--------------------------------------------------------------------------
| Registration & Login Controller
|--------------------------------------------------------------------------
|
| This controller handles the registration of new users, as well as the
| authentication of existing users. By default, this controller uses
| a simple trait to add these behaviors. Why don't you explore it?
|
*/
use AuthenticatesAndRegistersUsers,
ThrottlesLogins;
/**
* Create a new authentication controller instance.
*
* #return void
*/
public function __construct() {
$this->middleware('guest', ['except' => 'getLogout']);
}
/**
* Get a validator for an incoming registration request.
*
* #param array $data
* #return \Illuminate\Contracts\Validation\Validator
*/
protected function validator(array $data) {
return Validator::make($data, [
'name' => 'required|max:255',
'email' => 'required|email|max:255|unique:users',
'password' => 'required|confirmed|min:6',
]);
}
/**
* Create a new user instance after a valid registration.
*
* #param array $data
* #return User
*/
protected function create(array $data) {
return User::create([
'name' => $data['name'],
'email' => $data['email'],
'password' => bcrypt($data['password']),
]);
}
protected $redirectPath = '/dashboard';
}

Answer 1

Here is one way of doing it.
$user = new \User($data)->save();
$user_detail = new \UserDetail($detail_data);
$user->user_detail()->associate($user_detail);

Answer 2

Okay, I think #ajameswolf method is to update data. What I need is to create a data in two table which have relation.
I use this method in my AuthController.
protected function create(array $data) {
$user = User::create([
'name' => $data['name'],
'email' => $data['email'],
'password' => bcrypt($data['password']),
]);
$user_detail = UsersDetail::create([
'birthOfDate' => null
]);
$user->save();
$user_detail->save();
return $user;
}